There are three of us that I know of who are experiencing a problem initiating a slew in Stellarium. We are all using iOptron CEM60 mounts with the latest versions of Commander, firmware and ASCOM driver. One of us is running Windows 10 Pro, one Win 10 Home and one sometimes run Win8 or Win 10. All of us originally used Stellarium Scope, one of us has reverted to Stellarium Scope. The problem goes back at least one Stellarium revision.
The problem manifests when you select a target and initiate a slew, with the move mount dialog. Nothing happens, then when you give up and close the dialog box, the mount slews. Sometimes the keyboard short cut, cntrl 1 works, sometimes not. Occasionally closing Stellarium will start the slew. While waiting for the slew iOptron Commander does not show any failed messages.
Sometimes the problem occurs once and then not again during a session. Sometimes in a long session it will eventually reoccur.
The common behavior is that one or more target slews, no matter how initiated either does not begin, begins after you close Stellarium or some routine in Stellarium is closed. One of us reports that sometimes a slew will stop before it reaches the target, then start again without any input and finish the slew.
The PCs are running Intel chipsets of different vintages, >5 years old, about 5 years old, and less than 2 years old. All of them have 16GB of memory.
The other astronomy software in use with Stellarium includes PHD2, SharpCap4 64 bit, ASI Studio and Astro Toaster. Two of us will sometimes use the hand controller to initiate a target go to, one of us does not.
Looking for an easy solution of course but failing that a suggestion on how to best bring this the Stellarium Team.
None of us knows beans about C++ and we have no useful speculation to offer. It may be peculiar to the iOptron firmware or the iOptron Commander or the iOptron ASCOM driver. It is not from what I am told a problem with other mounts, but then we don't know everyone who has every other mount and uses Stellarium.